GB2053562A - Discharge Lamp - Google Patents

Abstract

The present invention provides an electric discharge lamp for irradiation purposes, comprising a discharge vessel which transmits ultra-violet radiation, electrodes, a noble gas filling and at least one buffer gas or buffer vapour, wherein the discharge vessel contains lutetium and/or a lutetium compound.

Description

SPECIFICATION Electric Discharge Lamp The present invention is concerned with an electric discharge lamp which can be used both for general irradiation purposes, for example for health and cosmetic irradiation, as well as in therapy of skin diseases, for example, psoriasis or acne. The lamp can also be used in technical apparatus, for example for copying purposes.

It is known to use ultra-violet irradiation to produce heaith-giving and cosmetic effects and to cure skin diseases by phototherapeutic and photochemotherapeutic methods. More particularly, in the treatment of the various forms of psoriasis, phototherapy and photochemotherapy can produce considerable improvements.

Photochemotherapy is a combination therapy which is based on the use of a medicament as a photosensitiser, followed by irradiation, mainly in the long wave ultra-violet range (Wolff et al., Dtschl. Med. Wschr., 124,2471/1975).

In phototherapy, which is generally known-as selective phototherapy, the therapeutic effect is initiated, without sensitisation with a medicament, by the direct attack of energy-rich ultra-violet radiation (UV-B/C) on the genetic material of the epidermis (Trennier et al., Akt.

Derm. 3, 49/1977; Schröl, Dt. Dermatologie, 25, 499/1977).

For both types of therapy, various irradiation apparatus are known, for example, those disclosed in Federal Republic of Germany Patent Specifications Nos. 2,707,920; 2,707,908; 2,609,273 and 2,616,892. The radiators used nowadays are not only special low pressure fluorescent lamps but, more particularly, xenon high pressure lamps and/or mercury vapour high pressure discharges, and also discharges in halogen-metal vapours, for example, iron- gallium iodide and gallium-indium- samarium-lead iodide, as disclosed in Federal Republic of Germany Patent Specification No.

2,531,876.

A lamp has also been suggested for the abovementioned irradiation purposes which, in the discharge vessel, contains the elements copper and/or silver and/or compounds thereof, as disclosed in German Democratic Republic Patent Specification No.211,140.

That method has the disadvantage that, in the relevant temperature range, mercury halides have a high stability, so that metallic copper or silver may be deposited on the wall. The addition of, for example, xenon, cadmium iodide or zinc iodide is necessary to avoid these deposition processes but this increases the technical costs.

An analysis of the results with regard to the optimum range of the spectrum for the majority of irradiation purposes showed that the range extends from 320 to 340 nm, the range from 320 to 330 nm having the greatest importance.

If this favourable spectral range is filtered out, using appropriate filters, only low irradiation strengths are, nevertheless, obtained with the known light and radiation sources so that, in practice, the use of conventional lamps does not give the desired result.

It is an object of the present invention to provide a radiation source with a particularly strong emission in the therapeutically and also cosmetically favourable spectral range above 320 nm.

The problem with which the present invention is concerned is to provide an electric discharge lamp of highly concentrated power which emits a particularly large amount of energy in the wave length range of from 320 to 340 nm.

The present invention is based on the fact that the element lutetium, which has a spectrum with many lines but has readily excitable lines at 328 nm, 328.2 nm, 331.2 nm, 336 nm, 337.7 nm, 338.6 nm and 340 nm, has a considerable proportion of the emission in the required area of the spectrum.

Thus, according to the present invention, there is provided an electric discharge lamp for irradiation purposes, comprising a discharge vessel which transmits ultra-violet radiation, electrodes, a noble gas filling and at least one buffer gas or buffer vapour, wherein the discharge vessel contains lutetium and/or a lutetium compound.

When a lutetium compound is present in the discharge vessel, this is preferably a halide.

With the radiator wall temperatures of 800 to 1200 K, which can be achieved in practice, the lutetium halides have high enough vapour pressures to transport adequate quantities of the rare earth metal into the discharge path where, due to the low excitation energies, there are satisfactory conditions for a strong emission. The saturation vapour pressure of Flu13, for example, can be approximated by log pA--B/T, where p is obtained in Pa, if 1.873, B=10163, and the temperature is expressed in K. For the usual wall temperature of 1000 K, this gives a vapour pressure of about 50 Pa.

If desired, the discharge vessel may contain at least one further metal and/or metal compound, which is preferably a halide. The additional introduction of indium, preferably in the form of a halide, into the discharge vessel also has an advantageous effect. The strong indium lines at 325.6 and 325.8 nm clearly contribute towards increasing the emitted energy in the required region of the spectrum.

The effect of considerable contraction of the column, known from investigations of various rare earth metal iodides in buffer vapours, for example Dyl3 in mercury, do not occur when lutetium was used. It proved possible to discharge lutetium into the mercury vapour in a stable manner for a prolonged period of time.

The temperature profile of the discharge can also be further flattened with caesium and/or rubidium and/or potassium and/or a compound of these elements, which has a positive influence on the emergence of ultra-violet radiation from the column.

It has also proved advantageous, for the long term stability of the lamp according to the present invention, when the electrodes, which normally consist of pure or thoriated tungsten, contain lutetium oxide.

The following Examples are given for the purpose of illustrating the present invention: Example 1 A discharge vessel of silica glass or ultra-violet permeable ceramic with an internal diameter of 12.5 mm. and an electrode distance of 25 mm.

was filled with 4000 Pa of argon, 20 mg. of mercury and 3 mg. of lutetium iodide (flu13).

After a warming up time of 1 5 minutes on a 220 V mains supply with an appropriate connecting device, a power of 250 W was obtained at a voltage of 11 5 V on the radiator.

The radiation emitted was made up of the known lines of mercury and the spectrum of lutetium, consisting of many lines. A large proportion of the energy was emitted in the frequently desired spectral region of from 320 to 340 nm. Since radiation was produced very efficiently even beyond 340 nm, a radiator of this kind could be used either as a wide band radiator or, with appropriate filters, as a radiation source for emission in predetermined limited spectral regions.

Example 2 A discharge vessel of silica glass or ultra-violetpermeable ceramic with an internal diameter of 22 mm. and electrodes containing lutetium oxide (Lu203) as the emitter and with an electrode distance of 85 nm was filled with 2500 Pa of argon, 45 mg. of mercury, 3 mg. of lutetium, 13 mg. of mercury iodide (Hgl2) and 5 mg. of rubidium iodide.

After a warming up time of 30 minutes on a 220 V mains supply with an appropriate connecting device, a power of 1 kW was obtained at a voltage of 11 5 V on the radiator. The discharge was diffuse, producing particularly satisfactory conditions for the excitation and emergence of the ultra-violet radiation.

Example 3 A discharge vessel of silica glass or ultra-violetpermeable ceramic with an internal diameter of 25 mm. and an electrode distance of 125 mm.

was filled with 2500 Pa of argon, 175 mg. of mercury, 1 5 mg. of lutetium iodide, 1 mg. of indium iodide (Inl) and 7 mg. of caesium iodide.

After a warming up time of 15 minutes on a 380 V mains supply with an appropriate connecting device, a power of 2 kW was obtained at a voltage of 230 V on the radiator. The discharge was diffuse, the radiation perceptible as light being bluish. The addition of indium gave the spectrum additional lines at 325 nm, so that almost continuous radiation energy was available from 325 to 340 nm and beyond. Since the emitted radiation was produced with high efficiency, high irradiation strengths could also be obtained, even after possibly necessary filtering.

Such radiators were extremely useful for the selective phototherapy of skin diseases.

Example 4 An electrical discharge vessel of silica glass having an internal diameter of 15 mm. and an electrode distance of 2.5 mm. was filled with 7000 Pa of argon, 70 mg. of mercury, 2 mg. of lutetium iodide, 0.5 mg. of potassium iodide and 0.1-mg. of indium iodide.

After a warming up time of 15 minutes on a 220 V mains supply with an appropriate connecting device, a power of 200 W was obtained at a voltage of 55 V on the radiator. A favourable spectrum was observed similar to those of the preceding Examples. The emitted radiation could be particularly satisfactorily concentrated due to the small distance between the electrodes of this discharge.

Claims (8)

Claims

1. An electric discharge lamp for irradiation purposes, comprising a discharge vessel which transmits ultra-violet radiation, electrodes, a noble gas filling and at least one buffer gas or buffer vapour, wherein the discharge vessel contains lutetium and/or a lutetium compound.

2. An electric discharge lamp according to claim 1, wherein the lutetium compound is a lutetium halide.

3. An electric discharge lamp according to claim 1 or 2, wherein the discharge vessel contains at least one further metal or metal compound.

4. An electric discharge lamp according to claim 3, wherein the further metal compound is a halide.

5. An electric discharge lamp according to claim 3, wherein the discharge vessel contains indium and/or an indium compound, in addition to the lutetium and/or lutetium compound.

6. An electric discharge lamp according to claim 3, wherein the discharge vessel contains caesium and/or rubidium and/or potassium and/or a compound of those elements in addition to the lutetium or the lutetium compound.

7. An electric discharge lamp according to any of the preceding claims, wherein the electrodes disposed in the discharge vessel contain lutetium oxide.

8. An electric discharge lamp according to claim 1, substantially as hereinbefore described and exemplified.